Double acting two stroke cycle internal combustion engines



A. E. BROWN Sept. 12, 1967 Filed Oct. 18, 1965 5 Sheets-Sheet l v 5 4 l 7 7 X/ o W 7 6 N 2 5 m 7 T S 6 A C f 4 II A ll 22/3 3 u V i 6 A m ,W/Z/Q/ A I R SU P PLY MEANS WEB mum Sept. 12, 1967 ,E,BROW N 3,340,856

DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINES Filed Oct. 18, 1965 5 Sheets-Sheet 2 Sept. 12, A. E. BRQWN DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINES Fi led Oct. 18, 1965 5 Sheets-Sheet 5 II FIG-m1 FIG-1E A. E. BROWN Sept. 12, 1967 DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINES Filed Oct. 18, 1965 5 Sheets-Sheet 4.

FIG-X FIG-XIII llllllll.

. FIG-IE A ////////////AA///////// mas/mm Se t. 12, 1967 A. E. BROWN 3,340,856

DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINES Filed Oct. 18, 1965 5 Sheets-Sheet 5 .l |||t 4 EE AI R SUPPLY MEANS United States Patent I DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINES Arthur E. Brown, 117 E. th St., Corning, N.Y. 14830 Filed Oct. 18, 1965, Ser. No. 497,230 11 Claims. (Cl. 123-61) ABSTRACT OF THE DISCLOSURE A reciprocating double acting stepped piston uncovers inlet ports and exhaust ports at each end of its stroke to obtain uniflow type scavenging operations. When starting, the engine may run single acting and serve as its own scavenge pump until suflicient speed is attained. Thereafter, the engine may run double acting using auxiliary means for supplying fresh charges of air or fuel-air mixture.

crankcase casting to be relatively simple even though the engine is double acting.

These engines are well suited for small to medium size applications and would have their best use in powering boats, chain saws, portable pumps, portable electric plants, drone planes, small helicopters, and other applications where light weight and compact size are important.

General advantages of these engines The engines described herein have the following group of advantages (1) to (9) over conventional engines now in general use. These nine advantages indicate powerful reasons for making progress on these engines and for at-- tacking the problems associated with them.

1) Theengines have two power strokes per rotation of each crankand connecting rod. This permits fewer cylinders for a given power output and/ or smoother running.

(2) The engines have uniflow type scavening (instead of cross flow or loop scavenging) and this secures a better flow pattern with less eddy currents, less mixing with exhaust gas, and less short circuiting of the scavenge air.

(3) The exhaust ports can be made shorter in height because they extend around the full periphery of the cylinder instead-of part way around as in a cross or loop scavenged engine. Thus the expansion stroke is longer and B.M.E.P.- higher.

(4) The engines are well suited for high rpm; becauseof uniflow scavenging and large port areas. Also, the reciprocatinginertia forces are cushioned at each end of each stroke by a gas pressure force and this reduces the bearing loads at high speed.

" (5) .The engines are double acting, yet no cross heads,

cross head guides, piston rods, or stufiing boxes are required.

(6) Not required are power poppet valves, power cams, power cam shafts,.power rocker arms, or power push rods.

(7) The cylinders andv pistons are substantially concentric. about their axis. The gas flow and thecombustion is concentric about the cylinder axis. Therefore, the thermal expansion of these parts will be substantially concentric so as to reduce out of round distortion.

The above is in contradistinction to nonconcentric engines such as loop scavenged engines in which cooled inlet ports and hot exhaust ports are located on opposite sides of the cylinder.

(8) The peak bearing loads are lower because the reciprocating inertia forces are opposed at each end of each stroke by a gas pressure force. (9) Because of advantages (1) 'to (8) 'above, the en- A special head insert permits the. cylinder block and 3,340,856- Patented Sept. 12, 1967 gines can be more compact, lighter in weight, lower in initial cost, and lower in maintenance.

As an indication of compactness, a single crank and a single double acting cylinder is drawn full scale in FIG. I within an 8 x 11% inch border. One double acting cylinder has a displacement volume of 28.4 cubic inches.

Specific objects and advantages of this invention A principal object is to provide an improved means for supplying scavenge air during starting and low power operation of the engines. ,1

The front valve piston 1 must be large enough in diameter to avoid interference with the connecting rod 2. It is an object however, to retain the diameter of the valve piston 1 at a minimum so-as' to obtain a maximum displacement of the working chambers 3 and 4 for a given diameter of the working piston 5.

Another object is to locate the wrist pin 6 in the working piston 5 (instead of in the front valve piston 1). This secures seven important advantages (a) to (g) which are subsequently described in detail.

Another object is to provide two novel mounting and retaining arrangements for the wrist pin 6 which permit the wrist pin to be located in the working piston 5 yet which do not interfere with the functioning of the three piston rings 7, 8 and 9.

which is shaped such that there is a minimum of eddy currents and air-exhaust mixing during each scavenging An advantage of this invention is that each double acting cylinder requires only a single exhaust connection and a single inlet connection. This reduces the manifolding required and simplifies the engine in general.

Another object is to provide a double acting engine wherein the cylinder block and the upper half of the crankcase can be made as an integral casting. In present single acting engines, the advantages of making the crankcase and cylinders a single cast structure are well known. These advantages are: 1) a lighter weight but more rigid structure, (2) more compact through elimination of flanged joints, (3) lower cost automatic machining of parallel cylinder bores in a transfer machine, (4) less assembly cost, (5) fewer parts and fewer machining operations, and (6) better controlof machining tolerances. This invention now secures the above six advantages in a double acting engine.

Another object is to provide a double acting engine wherein the integral cylinder block and crankcase casting is no more complex than'the similar casting in present single acting engines. This object is obtained through the use of novel inserted front cylinder heads 10.

Another object is to permit assembly of the engines even though the working cylinder is integrally cast to part of the crankcase.

Another object is to improve thermal efiiciency by employing uniflow type scavenging in place of cross flow or loop scavenging Theflow of scavenging air (or fuelair mixture) through each working chamber is substantially unidirectional and this reduces eddy currents, mix ing, and short circuiting. In conventional carburator type cross scavenge and loop scavenge engines, a substantial portion of the inlet flow is short circuited to the exhaust ports so that unburned carburated fuel is lost out the exhaust port. This is the principal reason why cross scavenged carburator engines show a poor thermal efiiciency compared with four stroke cycle engine's.

Another object is to provide a novel sleeve-liner -77 which performs multiple functions as will be explained. Another object is to provide a combustion chamber operation.

Another object is to provide an unusually long connecting rod which secures 6 advantages subsequently described in detail.

Brief description of the drawings FIG. I is a sectional view of one form of the invention.

FIG. II is a section view of the same engine shown in FIG. I taken through the axis of the crankshaft and through the axes of the two working cylinders. Only the bottom portion of the engine is shown in FIG. II.

FIG. III is a section view of the reciprocating parts for the engine shown in FIG. I. The section is taken through the axis of the wrist pin.

FIG. IV is a transverse section view of the parts shown in FIG. III. The section is taken through the axis of the wrist pin and perpendicular to the axis of the piston assembly.

FIG. V is an elevational view of the parts shown in FIG. III.

FIG. VI is a larger scale isometric view of a plug 11 for use in the assembly shown in FIGS. III and IV.

FIG. VII is a larger scale isometric view of a taper pin 12 for use in locking and locating the plug 11.

FIG. VIII is a sectional view of an alternate piston construction for the engine shown in FIG. 1.

FIG. IX is a sectional view of an alternate form of engine.

FIGS. X and XI are diagrams illustrating the effects of locating the wrist pin in the working piston and the front valve piston.

Identical parts are given the same reference numbers.

General description and operation Throughout the description and claims, the front of the engine is defined as being nearer the crankshaft than the back. Also, the term outward stroke means to move away from the crankshaft and inward stroke means to move toward the crankshaft.

Referring to FIGS. I and II, a crankshaft 13 (having crankpins 14) is mounted in the crankcase 15. Connecting rods 2 and wrist pins 6 interconnect the pistons and crankshaft. The working cylinders 16 are integrally cast to the top half 17 of the crankcase. The inserted front heads have front valve cylinder bores 18 formed therein. The back head 19 has back valve cylinder bores 20 in the head structure. Each double acting Working piston 5 has a front valve piston 1 and a back valve piston 21 integrally cast to it. The pistons reciprocate in their respective cylinders. An air supply means is shown schematically at 22 for the purpose of supplying scavenge air. The air may be introduced through the interior of the crankcase at 23 or an alternate method is to introduce the scavenge air through the back cylinders at the reed valves 24 in the plate 25.

A carburator (not shown) may be located ahead of or after the air supply means. If desired, lubricant may be mixed with the liquid fuel as is common practice in many two-stroke cycle engines.

When near top dead center stroke position, the Working pistons 5 uncover the exhaust ports 26 and the front valve pistons 1 uncover the front inlet ports 27 so as to obtain a uniflow type scavenging operation of the front working chambers 3. When near bottom dead center, the back valve pistons 21 uncover the back inlet ports 28 and the Working pistons uncover the exhaust ports 26 so as to uniflow scavenge the back working chambers 4.

Liquid cooling passages are indicated at 29. With proper fins, the engine can be made air cooled.

Discussion of scavenge air supply means 22 It is preferred that the scavenge air supply means be simple, compact, light weight, and low cost. One possible means would be a centrifugal blower driven by a speed up toothed belt from the engine crankshaft. A second type would be to employ Kadenacy type scavenging wherein the inertia of an outrushing mass of exhaust gas is used to draw a fresh change into the cylinder. A third (but more expensive) type would be to employ a turbo-charger wherein a centrifugal blower is driven by an exhaust powered turbine.

Methods of starting the engines In all three of the above described means for supplying scavenge air, it is difficult to start the engine without employing a separate air supply during starting. In the case of a belt driven centrifugal blower, the applicant has found by experiment that during starting, the output pressure of the blower is very low and a hand start is virtually impossible. With either Kadenacy scavenging or a turbocharger, there is no exhaust gas energy during starting hence a simple hand start is impossible as far as the applicant knows.

In order to alleviate the above startingproblem, the following described arrangement is provided: When starting, the poppet valve 30 (FIG. I) is moved and set in an open position and the electrical switch 31 is opened so as to eliminate spark to the ignition plug 32. Under these conditions, the engine is able to operate single acting with the back working chamber 4 serving as a scavenge pump for supplying air to the front working chamber 3. An inward stroke of the pistons draws air (or a fuel-air mixture) through the reed valve 33, into the crankcase interior 34, up through the hollow piston passage 35, through the passage 36, through poppet valve 30, and into the back working chamber 4. (An alternate method is to draw air through the reed valve 24.) On outstroke,the reed valve 33 closes and the volume in the back working chamber 4 passes back through the open poppet valve 30 and the air is slightly compressed into the hollow interior of the piston assembly and the interior of the crankcase. Each crank chamber is compartmented as is done in present single acting engines. Near top dead center, the front inlet ports 27 are uncovered so as to unifiow scavenge the front working chamber 3.

After the engine has started and is running single acting at a nominal speed, then the engine is capable of running double acting using the separate air supply means 22 as a source of scavenge air. This is because there is then sufficient blower pressure (if a centrifugal blower is used) or sufficient energy in the exhaust (if Kadenacy scavenging or a turbocharger is used). Double acting operation is initiated by releasing the linkage 37 (so as to close the poppet valve 30) and by closing the electrical switch 31 (so as to restore spark to the ignition plug 32)..

After starting the pin 38 may be depressed so as to hold the reed valve 33 off its seat and thereby obtain less flow resistance.

The back side of poppet valve 30 is indicated by the number 39.

The purpose of the electrical switch 31 is to prevent unwanted ignition of the fuel-air mixture during single acting operation.

Refer to FIG. IX which illustrates a starting scheme similar to that shown in FIG. I except the front Working.

chamber 40 serves as a scavenge pump for the back working chamber 41 during starting and low power operation. After starting, the lever 42 is released (so as to close poppet valve 43) and the electrical switch 44 is closed whereupon the engine is able to run double acting. The end cap 45 is placed on and reciprocates with the back valve piston 46 so as to gain more displacement of scavenge air during starting and low speed operation. If desired, the cap 45 may be dispensed with and a plate (similar to 25 in FIG. I) attached to the end of the back valve cylinder 47.

It is noted that in both FIGS. I and IX the engines run single acting during starting. In FIG. I, the displaced volume of scavenge air (during starting) is equal to the displacement volume of the front working chamber 3. In.

Discussion of wrist pin location A feature of this invention is the location of the wrist pin 6. In Patents 2,780,208 and 2,918,045 the wrist pin was located in the front valve piston. However, it has since been concluded that it is much better to locate the wrist pin wtihin the working piston 5 because of the following advantages and objectives (a) to (g);

(a) The piston assembly reciprocates in the cylinders with low uniform side pressure and with no tendency to tilt, ride hard, or scuff in the cylinders. FIGS. X and XI are diagrams which illustrate the effects of locating the wrist pin respectively in the working piston and the front valve piston. The forces F and F represent in each case the sidewise force component on the wrist pin due to angularity of the connecting rod. For purposes of illustration, the clearances between parts and the misalignment has been exaggerated. In FIG. X, the side force F causes the working piston to ride fiat against the cylinder wall with less tendency to tilt, ride hard, or scuff. In FIG. XI, the side force F causes the piston assembly to tilt as shown. The pistons are shown to ride hard at edges 48 and 49.

(b) It is required that the wrist pin bearing 50 be sufficiently large in size so as to reliably withstand the forces imposed on it. By locating the wrist pin within the working piston 5 (instead of in the front valve piston 1) there is more space available and it is easier to secure this objective.

(c) It is required that there be adequate area for the flow of scavenge air through the pistons and past the wrist pin. FIG. IV illustrates the large flow areas 51 past the wrist pin. If the wrist pin was not located as shown (but instead was located within the front valve piston 1) then these large flow areas 51 would not be available. The pistons are internally cooled by the flow of air through them.

(d) The wrist pin 6 is not located within the front valve piston 1 and therefore there are no alternating tension and compression loads (due to gas pressure forces) in the front valve piston. This means therefore that the front valve piston 1 can have relatively thin walls and be light in weight. Also, there are no dangerous stress concentrations at the corner juncture 52 where the valve piston joins the work-ing piston.

(e) If the wrist pin were located in the front valve piston 1, then the wrist pin hole would be directly exposed to the front working chamber 3 and the high pressure high temperature combustion gas therein. This would create the problem of how to prevent leakage of combustion gas through the wrist pin hole to the interior of the pistons. Such leakage would be undesirable since it would tend to contaminate and overheat the wrist pin bearing.

However, by locating the wrist pin in the working piston (as described), this problem has been virtually eliminated because the wrist pin hole 53 is sealed on each side by the piston rings 7 and 9. Furthermore there is.

sufiicient radial space available to incorporate the plugs 11 which seal off any gas which may escape past the end piston rings 7 and 9.

(f) In order to mount the wrist pin 6 in the working piston (as specified in the above objectives (a) to (e) it is necessary to make the connecting rod 2 unusually long. The con rod shown in FIG. I has a ratio of length to crank radius of 6.3 whereas the most common ratios are 4 to 5. The long con rod has the advantage that the side thrust on the pistons is low due to the small angularity of such a long con rod.

(g) The long con rod also has the advantage that the secondary reciprocating inertia forces are low. If the con rod were infinitely long (to illustrate the extreme case), then the piston motion would be simple harmonic and the secondary inertia forces would be zero.

Discussion of con rod length v.It is an object to retain the diameter of the valve piston 1 at a minimum so as to obtain a maximum displacement of the working chambers 3 and 4 for a given diameter of the Working piston 5. However, the front valve piston 1 must be large enough in diameter to avoid interference with the con rod 2 when the pistons are near mid stroke position as shown in FIG. I. If the con rod were infinitely long (to illustrate an extreme case) then the top end of the con rod would have zero angular motion and the valve piston 1 could be made smaller in diameter and there would be no interference between the piston and the side of the con rod. An infinitely long con rod is impractical of course. The applicant has found that in this particular type of double acting engine a con rod whose length is 6 to 8 times the crank radius is a good proportion to work with and this has the following ad vantages (l) to (6):

(l) The wrist pin may be mounted in the working piston 5 (instead of the front valve piston) and this secures the advantages previously mentioned for that feature.

(2) The valve piston 1 can be reduced in diameter since a long con rod has less angular motion.

(3) There is less piston side thrust due to the small angularity of such a long con rod.

(4) The secondary inertia forces are less and this aids balancing in most cases.

(5) With a long con rod, the acceleration of the pistons is more nearly equal at top and bottom dead center stroke positions. This is not of much consequence in a single acting engine, but in a double acting engine, this means that the porting (and hence scavenging) is more nearly equal between top and bottom dead center stroke positions.

(6) Engine designers are sometimes faced with the problem of interference between counterweights and the bottom of a piston when the piston is at bottom dead center position. This problem is not present in this engine due to the unusally long con rod.

Mounting arrangement for the wrist pin the wrist pin hole and locked in place with the taper dowel pins 12 and set screws 54. Since the plugs 11 fit tightly into the wrist pin hole, there is no leakage of combustion gas at this location from one piston ring to another. Furthermore, there is no volumetric pocket or space (at the ends of the wrist pin hole) for leakage gas to flow into.

As far as the piston rings are concerned, the skirt of the piston is a solid unbroken piece of metal and the rings do their sealing job as though there were no wrist pin hole' at all. It is thus seen that this method of mounting the 60. wrist pin does not interfere with the sealing capability of the three piston rings.

FIGS. V and VI illustrate how a portion of the center ring groove 55 passes through the ends of the plugs 11.

The outer diametral surface 56 of the piston and the' ring grooves should be finish machined with the plugs 11 doweled in place. This procedure permits the plug end surface 57 and the groove 55 to be formed while machining the piston and thereby eliminates additional machining is married to its respective piston, however, and is ordinarily not interchangeable with plugs from other pistons. The taper pins 12 serve to locate the plugs 11 in such a manner that they cannot work loose nor can they rotate 5 and bind the center piston ring 8. It is noted that the plugs 11 also serve to axially retain the wrist pin 6 so that no other form of endwise retention for the wrist pin is required.

FIG. VIII illustrates an alternate mounting arrangement for the wrist pin and piston rings. In FIG. VIII, the left half of the section view taken along the axis of the wrist pin and the right half is taken perpendicular to the axis of the wrist pin. A collar 58 is pressed onto the body of the working piston and held in place by several dowel pins 59. Ring grooves are machined in the collar so as to carry the two piston rings 60 and 61. The collar also serves to axially retain the wrist pin 6 so that no other form of endwise retention is required. This mounting arrangement also permits the wrist pin to be located and installed within the working piston yet there is no loss in sealing capability of the three piston rings, 60, 61 and 62.

Discussion of cylinder block and crankcase It is common practice with single acting outboard marine engines to form the cylinder block and one half of the crankcase as an integral casting since this leads to a low cost, rigid, compact, and lighter weight construction. It is an object of this invention to do the same thing and secure the same advantages in a double acting engine.

- Referring to FIGS. I and II, the cylinder block 63 and the upper half of the crankcase are cast integral in a conventional manner. The front cylinder heads are in the form of separate pieces which are inserted into the working cylinders 16. The heads 10 rest against the shoulders 64 and are retained by dowel pins 65. Seal rings 67 seal the combustion gas pressure. An advantage of this arrangement is that the cylinder block and crankcase casting is no more complex than (and is similar to) the cylinder block and crankcase casting in present single acting engines.

, The cast iron liners 68 for the Working cylinders are cast into the aluminum block structure 63.

FIG. II shows how a cylinder block structure (containing two or more working cylinders) can be integrally cast to the upper half 17 of the crankcase and there is no difficulty in assuring (during manufacture) that each front valve cylinder 18 is concentric with its respective working cylinder 16. Concentricity is assured because the separate inserted front heads 10 are each located and contained by their own working cylinder.

' FIG. IX illustrates a construction in which both the working cylinder 16 and the front valve cylinder 18 are cast integral with the upper half 69 of the crankcase. This arrangement can also be employed where two or more working cylinders are integrally cast into the same cylinder block. The cast iron liners 66 and 68 would be cast into the aluminum block structure 70. The front inlet ports 27 and exhaust ports 26 would be preformed prior to casting into the block structure so as to permit ease of forming the ports. The liners 66 and 68 may be finish bored and honed on the same set ups so as to reduce cost and assure concentricity. It is necessary to pass the large end of the con rod 71 through the front valve cylinder 18 in order to assemble the engine. Therefore the con rod big end 72 is split on the bias so as to permit assembly.

Discussion of combustion chambers and sleeve liners Referring to FIG. II, the annular combustion chambers 73 have tapered conical surfaces 74. The inlet air (or fuel-air mixture) has a radial flow direction as it flows through the inlet ports 27. The tapered surfaces 74 smoothly deflect the incoming air from a radial flow direction to an axial flow direction so as to minimize the formation of eddy currents and so as to reduce mixing of the air with exhaust gas during each scavenging operation.

Referring to FIG. I, the sleeves 75 have inlet ports 28 passing through their walls and the sleeves serve to retain the expanding type seal rings 76 in their grooves when the valve pistons are near the bottom end of their reciprocative stroke. The sleeves are made integral with the liners 77. The front head 10 has a similar construction in regard to the sleeve-liners and combustion chamber shape. It is convenient to form the inlet ports 27 and 28 in the cast iron sleeve-liners prior to casting the sleeve-liners into head structures 10 and 19. The head structures may be made of cast aluminum alloy or other light metal.

The sleeve liners therefore perform a threefold function: (1) They retain the seal rings 76 so that they do not snap out of their grooves near the end of a stroke, (2) they serve as a wear resistant material for the seal rings 76 to ride against, and (3) they provide a convenient means for forming the inlet ports 28.

While the preferred embodiments of the invention have been described, it will be understood that the invention is not limited thereto since it maybe otherwise embodied within the scope of the following claims.

What is claimed is:

1. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted ins aid crankcase, a Working cylinder fastened to said crankcase, a valve cylinder fastened to said crankcase, said valve cylinder being smaller in diameter than said working cylinder, a double acting Working piston reciprocable in said working cylinder, a valve piston reciprocable in said valve cylinder, said valve piston being fastened to said working piston so as to form a reciprocating piston assembly, a connecting rod interconnecting said crankshaft and said piston assembly, said working cylinder having a front working chamber and a back working chamber inside it, said working cylinder having exhaust ports located in its wall, said working piston being adapted to control said exhaust ports, means for supplying scavenge air to said engine, said valve piston being adapted to admit scavenge air into said front working chamber, said front working chamber having a unifiow type scavenging operation exhausting through said exhaust ports, means for porting and scavenging said back working chamber, and said working cylinder Ibeing integrally cast to the upper portion of said crankcase, said valve cylinder is located in a separate head which is inserted into said working cylinder and fastened in place.

2. In a double acting two stroke cycle internal cornbustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a working cylinder fastened to said crankcase, a valve cylinder fastened to said crankcase, said valve cylinder being smaller in diameter than said working cylinder, a double acting working piston reciprocable in said working cylinder, a valve piston reciprocable in said valve cylinder, said valve piston being fastened to said working piston so as to form a reciprocating piston assembly, a connecting rod interconnecting said crankshaft and said piston assembly, said working cylinder having a front working chamber and a back working chamber inside it, said working cylinder having exhaust ports located in its wall, said working piston being adapted to control said exhaust ports, means for supplying scavenge air to said engine, said valve piston being adapted to admit scavenge air into said [front working chamber, said front working chamber having a uniflow type scavenging operation exhausting through said exhaust ports, means for porting and scavenging said back working chamber, and said working cylinder being integrally cast to the upper portion of said crankcase, the big end of said connecting rod is split on the bias so as to permit passage of the end of said connectmg rod through said valve cylinder during assembly of the engine.

3. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft r-otatably mounted in said crankcase, a working cylinder integrally cast to a substantial portion of said crankcase, a separate front cylinder head inserted into said working cylinder and fastened in place, said front cylinder head having a reduced diameter front valve cylinder bore therein, a reduced diameter back valve cylinder fastened to said working cylinder, a double acting working piston reciprocable in said working cylinder, a front valve piston reciprocable in said front valve cylinder, a back valve piston reciprocable in said back valve cylinder, said valve pistons being fastened to said working piston so as to form a reciprocating piston assembly, a connecting rod interconnecting said piston assembly and said crankshaft, said working cylinder having exhaust ports located in its wall, said working piston being adapted to control said exhaust ports, means for supplying scavenge air, each valve piston being adapted to admit scavenge air into said working cylinder, and said working cylinder having uniflow type scavenging operations exhausting through said exhaust ports.

4. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a working cylinder fastened to said crankcase, a front valve cylinder and a back valve cylinder fastened to said working cylinder, said valve cylinders being smaller in diameter than said working cylinder, 21 double acting working piston reciproczrble in said working cylinder, a front valve piston reciprocable in said front valve cylinder, a back valve piston reciprocable in said back valve cylinder, said valve pistons being fastened to said working piston so as to form a reciprocating piston assembly, a connecting rod interconnecting said crankshaft and said piston assembly, said working cylinder having a front working chamber and a back working chamber inside it, said working cylinder having exhaust ports located in its wall, said working piston being adapted to control said exhaust ports, means for supplying scavenge air to said engine while running double acting, each valve piston being adapted to admit scavenge air to its respective working chamber, each working chamber having a uniflow type scavenging operation exhausting through said exhaust ports, said engine being adapted to operate single acting during starting and low power operation, one of said working chambers being hereby designated chamber A and the other said working chamber being hereby designated chamber B, chamber A serving initially as a scavenge pump for supplying scavenge air to chamber B during starting and low power operation of the engine, a first valve in communication with chamber A, said first valve being closed during double acting operation of the engine, means for holding said first valve open during starting and low power operation of the engine, passage means for conducting scavenge air from said first valve to chamber B, a second valve adapted to admit air to the interior of chamber A during a stroke of said piston assembly, and said second valve serving to prevent the escape of scavenge air (to the atmosphere) during a reverse stroke of said piston assembly.

5. The combination recited in claim 4 wherein said back working chamber is said chamber A and wherein said front working chamber is said chamber B.

6. The combination recited in claim 5 wherein said second valve is a pressure actuated valve and wherein means is provided for holding said second valve in a continuously open position during double acting operation of said engine.

7. The combination recited in claim 4 wherein said front working chamber is said chamber A and wherein said back working chamber is said chamber B.

8. The combination recited in claim 7 wherein said second valve is a pressure actuated valve and wherein means is provided for holding said second valve in a continuously open position during double acting operation of said engine.

9. The combination recited in claim 7 wherein a cap is fastened to the back end of said back valve piston with a gap located between the end of said back valve piston and the cap, said cap being reciprocable within said back valve cylinder, said cap forming a sliding seal with the wall of said back valve cylinder, and said cap serving as a scavenge pump for supplying additional scavenge air to said back working chamber during starting and low power operation of the engine.

10. The combination recited in claim 4 wherein a first ignition plug is located in firing communication with said front working chamber, a second ignition plug located in firing communication with said back working chamber, means adapted to turn off the ignition capability of one of said ignition plugs during starting and low power operation of the engine, and means to reinstate ignition capability of the ignition plug during double acting operation of the engine.

11. In a double acting two stroke cycle internal combustion engine, the combination of a crankcase, a crankshaft rotatably mounted in said crankcase, a working cylinder fastened to said crankcase, a front valve cylinder and a back valve cylinder fastened to said working cylinder, said valve cylinders being smaller in diameter than said Working cylinder, a double acting Working piston reciprocable in said working cylinder, a front valve piston reciprocable in said front valve cylinder, a back valve piston reciprocable in said back valve cylinder, said valve pistons being fastened to said Working piston so as to form a reciprocating piston assembly, said working cylinder having exhaust ports located in its wall, said working piston being adapted to control said exhaust ports, means for supplying scavenge air, said valve pistons being adapted to admit scavenge air into the interior of said working cylinder so as to obtain scavenging operations, said working cylinder having unifiow type scavenging operations exhausting through said exhaust ports, said valve pistons having grooves located in their outer diameters, expanding type seal rings located in said grooves, said seal rings being adapted to reciprocate inside said valve cylinders, said seal rings being adapted to seal against and ride against the walls of said valve cylinders, said valve cylinders being sufliciently long enough that said seal rings do not withdraw from said valve cylinders during each reciprocative stroke, a wrist pin located within said working piston, a connecting rod interconnecting said Wrist pin and said crankshaft for respective reciprocating and rotary motion, said connecting rod passing through the inside of said front valve piston, said front valve piston having a hollow interior for the passage of said connecting rod, and said connecting rod being sufficiently long enough and said front valve piston being sufliciently large enough in diameter such that the connecting rod clears said front Valve cylinder and said front valve piston during all rotative positions of said crankshaft.

References Cited UNITED STATES PATENTS 886,846 5/1908 Nicoll 123-61 1,699,171 1/ 1929 Waters 123-65 1,900,133 3/1933 Schaeifers 123-65 FOREIGN PATENTS 602,926 1/ 1926 France.

129,726 7/ 1919 Great Britain.

249,252 3/1926 Great Britain.

429,070 5/1935 Great Britain.

MARK M. NEWMAN, Primary Examiner. WENDELL E.- B'URNS, Examiner. 

4. IN A DOUBLE ACTING TWO STROKE CYCLE INTERNAL COMBUSTION ENGINE, THE COMBUSTION OF A CRANKCASE, A CRANKSHAFT ROTATABLY MOUNTED IN SAID CRANKCASE, A WORKING CYLINDER FASTENER TO SAID CRANKCASE, A FRONT VALVE CYLINDER AND A BACK VALVE CYLINDER FASTENED TO SAID WORKING CYLINDER, SAID VALVE CYLINDERS BEING SMALLER IN DIAMETER THAN SAID WORKING CYLINDERS BEING SMALLER IN DIAMETER THAN SAID SAID VALVE CYLINDERS BEING SMALLER IN DIAMETER THAN SAID WORKING CYLINDER, A DOUBLE ACTING WORKING PISTON RECIPROCABLE IN SAID WORKING CYLINDER, A FRONT VALVE PISTON RECIPROCABLE IN SAID FRONT VALVE CYLINDER, A BACK VALVE PISTON RECIPROCABLE IN SAID BACK VALVE CYLINDER, SAID VALVE PISTONS BEING FASTENED TO SAID WORKING PISTON SO AS TO FORM A RECIPROCATING PISTON ASSEMBLY, A CONNECTING ROD INTERCONNECTING SAID CRANKSHAFT AND SAID PISTON ASSEMBLY, SAID WORKING CYLINDER HAVING A FRONT WORKING CHAMBER AND A BACK WORKING CHAMBER INSIDE IT, SAID WORKING CYLINDER HAVNG EXHAUST PORTS LOCATED IN ITS WALL, SAID WORKING PISTION BEING ADAPTED TO CONTROL SAID EXHAUST PORTS, MEANS FOR SUPPLYING SCAVENGE AIR TO SAID ENGINE WHILE RUNNING DOUBLE ACTING, EACH VALVE PISTON BEING ADAPTED TO ADMIT SCAVENGE AIR TO ITS RESPECTIVE WORKING CHAMBER, EACH WORKING CHAMBER HAVING A UNIFLOW TYPE SCAVENGING OPERATION EXHAUSTING THROUGH SAID EXHAUST PORTS, SAID ENGINE BEING ADAPTED TO OPERATE SINGLE ACTING DURING STARTING AND LOW POWER OPERATION, ONE OF SAID WORKING CHAMBERS BEING HEREBY DESIGNATED CHAMBER A AND THE OTHER SAID WORKING CHAMBER BEING HEREBY DESIGNED CHAMBER B, CHAMBER A SERVING INITIALLY AS A SCAVENGE PUMP FOR SUPPLYING SCAVENGE AIR TO CHAMBER B DURING STARTING AND LOW POWER OPERATION OF THE ENGINE, A FIRST VALVE IN COMMUNICATION WITH CHAMBER A, SAID FIRST VALVE BEING CLOSED DURING DOUBLE ACTING OPERATION OF THE ENGINE, MEANS FOR HOLDING SAID FRIST VALVE OPEN DURING STARTING AND LOW POWER OPERATION OF THE ENGINE, PASSAGE MEANS FOR CONDUCTING SCAVENGE AIR FROM SAID FIRST VALVE TO CHAMBER B, A SECOND VALVE ADAPTED TO ADMIT AIR TO THE INTERIOR OF CHAMBER A DURING A STROKE OF SAID PISTON ASSEMBLY, AND SAID SECOND VALVE SERVING TO PERVENT THE ESCAPE OF SCAVENGE AIR (TO THE ATMOSPHERE) DURING A REVERSE STROKE OF SAID PISTON ASSEMBLY. 